Previous work on the role of Immune Complexes in the pathogenesis of Systemic Lupus Erythematosus will be continued. Primary emphasis will be placed on the isolation and characterization of undetermined types of complexes and certain low molecular weight anti-complementary substances that are detected in serum by precipitation with the C1q component of complement. In addition to studies on their role in the disease process, clues to possible etiologic agents will be sought in their composition. The possible relationship between the low molecular weight substances found in the serum of patients with the "SLE-Related-Syndrome" to those found in SLE will be studied. In addition, the possibility that acquired as well as genetic complement deficiency may predispose to SLE and SLE-like diseases will be explored. Other studies on immune complexes will focus on detection of complexes using new sensitive radioimmunoassays and the role of anti gamma globulins in a variety of immune complex nephridities. In addition, the recent finding that certain rheumatoid factors (RF) cross react with DNA-nucleoprotein (NP) will be pursued to determine if RF-NP complexes are involved in the pathogenesis of the diseases where such cross reactive rheumatoid factors occur.